1. Field of the invention
The present invention is related to a device for discriminating radar echoes according to their nature, to wit: ground echo, rain echo, sea echo, moving target echo etc. More particularly, the invention concerns fixed-unit meteorological radar installations wherein the echoes generated by rain must be distinguished from those generated by the ground, while these latter have to be eliminated.
2. Description of the prior art
In the prior art rain echoes or thick cloud echoes have been separated from fixed or stationary echoes (or targets) either by the so-called "circular polarization" method or by the so-called "MTI" technique (MTI standing for "Moving Target Indicator") involving phase measurement, or again by applying hypotheses concerning the length or the uniformity of the cloud or rain echoes.
Among these techniques only the first one is efficient, the second one giving variable and uncomplete results as regards the precipitations, while the third one never has completely satisfied the users.
U.S. patent specifications Nos. 4,139,847 and 4,318,100 disclose another principle which is based on the fact that those parameters defining the radar echo variations that are treated as random phemonena--i.e. the amplitude distribution and the autocorrelation (or self-correlation) function--have quite different values, depending on the nature of the echoes, and more particularly based on the fact that the received power of a stationary echo exhibits less average variation, and varies more slowly, than the received power of a rain echo does.
It is an object of the present invention to provide a radar echo discrimination device which achieves better performances than those of the devices disclosed in the above-mentioned U.S. patent specifications.